1. Field of the Invention
The present invention relates to a color image forming apparatus that uses an electrophotographic process etc.
2. Description of the Related Art
In an image forming apparatus that includes photosensitive drums for yellow (Y), magenta (M), cyan (C), and black (Bk) colors arranged in series, toner images of the respective colors are sequentially primary-transferred in a superimposed manner onto an intermediate transfer member. Then, the toner images are finally secondary-transferred together from the intermediate transfer member onto a recording medium. Such an image forming apparatus has been known as a copier or laser beam printer.
Toner remaining on the intermediate transfer member without being secondary-transferred from the intermediate transfer member to the recording material (hereinafter referred to as secondary-transfer residual toner) needs to be recovered from the intermediate transfer member before the toner images are secondary-transferred to the next recording material. As a configuration for recovering secondary-transfer residual toner, Japanese Patent Laid-Open No. 9-50167 discloses a configuration in which secondary-transfer residual toner is charged by a charging unit and recovered from an intermediate transfer member. Specifically, after the secondary-transfer residual toner is charged by the charging unit with a polarity opposite that of toner in a charged state during development, the charged secondary-transfer residual toner is moved from the intermediate transfer member to a photosensitive drum for recovery. The secondary-transfer residual toner moved to the photosensitive drum is recovered by a cleaning unit for the photosensitive drum.
Japanese Patent Laid-Open No. 2009-205012 discloses a configuration that uses a brush member as a charging unit. Secondary-transfer residual toner on an intermediate transfer member may be deposited in layers. To uniformly charge the secondary-transfer residual toner deposited in layers, the configuration disclosed in PTL 2 uses the brush member to charge the secondary-transfer residual toner deposited in layers on the intermediate transfer member while distributing the secondary-transfer residual toner.
However, adhesion of the secondary-transfer residual toner to the brush member may degrade the performance of charging the secondary-transfer residual toner. The degradation in charging performance of the brush member makes it difficult to equalize electric charges of the secondary-transfer residual toner. As a result, the secondary-transfer residual toner may not be able to be recovered from the intermediate transfer member.
The charging performance of the brush member may be degraded, because when the secondary-transfer residual toner is charged by the brush member, adhesion of the secondary-transfer residual toner is concentrated on the tips of conductive fibers of the brush member. If a large amount of secondary-transfer residual toner adheres to the tips of the conductive fibers, it is difficult to distribute the secondary-transfer residual toner deposited in layers on the intermediate transfer member, and is difficult to uniformly charge the secondary-transfer residual toner. If the secondary-transfer residual toner cannot be uniformly charged, it is difficult to recover the secondary-transfer residual toner from the intermediate transfer member.
This phenomenon tends to occur particularly when the electric charge of toner is low, or when the amount of secondary-transfer residual toner is increased by a reduction in transfer efficiency caused by use of paper with rough surface nature, such as rough paper.
In view of the circumstances described above, an aspect of the present invention is to provide an image forming apparatus that can suppress, even if secondary-transfer residual toner adheres to a brush member, concentration of the adhering secondary-transfer residual toner on the tips of the brush member, and can efficiently recover the secondary-transfer residual toner from an intermediate transfer member.